1. Technical Field
The present invention relates to an image reading apparatus.
2. Related Art
There is an image scanner (image reading apparatus) having an ADF (Auto Document Feeder) function (for example, JP-A-2007-201672). The image scanner reads the entire image of a document by an image sensor stopped while moving the document at a constant speed by rotating a sheet feeding motor.
The image scanner temporarily stores image data from the document in a buffer and sequentially transmits the image data to a host computer such as a personal computer (PC). A transmission speed is determined depending on the processing capability of the host computer. Therefore, a reading speed of the image scanner is adjusted to the degree that the buffer is not full.
However, even when the reading speed of the image scanner is adjusted, there are cases where the buffer becomes full. When the image scanner detects that the buffer is nearly full, the image scanner stops reading the image and the sheet feeding motor is stopped. After the full state of the buffer is released, the image scanner resumes the reading of the image.
Since the image data may not be transmitted to the host computer during the stoppage of the sheet feeding motor, the image data read before the stoppage of the sheet feeding motor has to be transmitted after the reading is restarted. In this case, since charges continue to be accumulated in the image sensor during the stoppage of the sheet feeding motor, dark noise may occur in the image data.
When LEDs (Light Emitting Diodes) of color to be lit are not lit at the time of resuming the reading, image data may not appropriately be read. However, the LEDs of colors to be lit (hereinafter, also referred to as “LED synchronization control”) are not prepared for lighting during the stoppage of the sheet feeding motor, and thus the lighting of the LEDs has to be prepared after the reading. Then, line missing may occur in the image data.